1. Field of the Invention
This invention relates generally to apparatus and methods for producing heat exchange with body tissue, and more specifically to methods and apparatus for the hypothermic treatment of a body fluid in a body conduit.
2. Discussion of the Prior Art
Many of the advantages of hypothermia are well known. By way of example, it has been found particularly desirable to lower the temperature of body tissue in order to reduce the metabolism of the body. In stroke, trauma and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. Hypothermia inhibits brain edema and lowers intracranial pressure.
In the past, hypothermic treatment has been typically addressed systemically, meaning that the overall temperature of the entire body has been lowered to achieve the advantages noted above. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. An example of this systemic approach includes catheters for transferring heat to or from blood flowing within a patient""s vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. A closed loop heat exchange catheter is also disclosed by Saab in U.S. Pat. No. 5,624,392. A cooling device for whole-body hyperthermia that utilizes the circulatory system of the body is known to be more efficient since the entire volume of the body is constantly perfused with the cold fluid at a capillary level.
Likewise, various other means of cooling the body have been tried with cooling blankets, ice water bladder lavages, ice baths, esophageal catheters and their associated methods. All of these devices require a considerable time to cool the body since the primary heat transfer occurs through the skin or the skull. A more efficient body cooling device that can quickly cool and accurately control the body temperature is required.
A heat exchange catheter and method of operation are included in the present invention. The method is adapted to produce hypothermia or hyperthermia, typically in a selected portion of the body without substantially varying the temperature of the remaining portions of the body. The selected body portion will usually be associated with a body conduit which conveys a body fluid to the selected body portion. Of particular interest are the organs of the body which are commonly nourished and maintained by a flow of blood in the arterial system. For example, a flow of blood is introduced to the brain through the carotid artery. Of course the temperature of this blood is usually at the normal body temperature.
By positioning a heat exchange catheter in the body conduit, heat can be added to or removed from the body fluid to heat or cool the selected body portion. For example, the heat exchange catheter can be disposed in the carotid artery where the arterial blood flowing to the brain can be cooled. The flow of cooled blood to the brain reduces the temperature of the brain thereby resulting in cerebral hypothermia. Importantly, this temperature reduction occurs primarily and selectively in the brain; the remaining portions of the body maintain a generally normal body temperature. In accordance with this method, the selected body portion, such as the brain, can be cooled thereby providing the advantages associated with hypothermia for this body portion. The remainder of the body, such as the portions other than the brain, do not experience the reduction in temperature. Furthermore, the invention is intended to remotely alter temperature in a region other than the point of introduction into the body. This is different than devices intended for systemic temperature control.
Several factors are of interest in effecting heat transfer in a heat exchanger. These factors include, for example, the convection heat transfer coefficient of the two fluids involved in the heat exchange, as well as the thermal conductivity and thickness of the barrier between the two fluids. Other factors include the relative temperature differential between the fluids, as well as the contact area and residence time of heat transfer. The Reynolds number for each fluid stream affects boundary layers, turbulence and laminar flow.
Notwithstanding the need for localized hypothermia, there will always be those procedures which call for systemic hypothermia. Many of the advantages associated with the present invention will greatly facilitate those procedures, for example, by decreasing the number and complexity of operative steps, increasing the heat transfer capacity of the device, and addressing other concerns such as the formation of blood clots.
In one aspect of the invention a catheter is provided with an elongate configuration, a proximal end and a distal end. An outer tube having a first lumen extends between the distal end and proximal end of the catheter, and an inner tube having a second lumen is disposed within the first lumen of the outer tube. Portions of the inner tube define a first flow path extending along the second lumen, while portions of the tubes define a second flow path extending between the first tube and the second tube. A plurality of hollow fibers provide fluid communication between the first and second flow paths, and a heat exchange fluid is disposed in the hollow fibers to cool the fibers.
In another aspect of the invention, a method for making a heat exchange catheter includes the steps of providing first and second tubes having first and second lumens, respectively. A plurality of hollow fibers are connected between a first flow path extending along the second lumen and a second flow path extending along the first lumen outwardly of the second tube. The method further comprises the step of insuring that the second tube is axially or rotationally movable relative to the first tube in order to vary the configuration of the hollow fibers.
In a further aspect of the invention, a method for operating a heat exchange catheter includes the steps of inserting into a body conduit the catheter with an inner tube disposed within an outer tube and defining a first flow path interiorly of the inner tube and second flow path between the inner tube and the outer tube. This inserted catheter also includes a plurality of hollow fibers disposed in fluid communication with the first and second flow paths. The method further includes steps for creating a flow of heat exchange fluid through the first and second flow paths, and moving the inner tube relative to the outer tube to change the profile of the hollow fibers.
In a further aspect of the invention, a heat exchange catheter includes an elongate shaft with first portions defining an inlet lumen and second portions defining an outlet lumen. A first manifold is disposed in fluid communication with the inlet lumen and a second manifold disposed in fluid communication with the outlet lumen. A plurality of hollow fibers are disposed between the manifolds in fluid communication with the inlet and outlet lumens. The catheter is adapted to receive a heat exchange fluid and to direct the heat exchange fluid through the hollow fibers to exchange heat through the hollow fibers.
In still a further aspect of the invention, a catheter is adapted to exchange heat with the body fluid flowing in a first direction through a body conduit. The catheter includes a shaft having an input lumen and an output lumen. A plurality of hollow fibers define a heat exchange region and collectively define an output surface of the heat exchange region. The input lumen of the shaft is coupled to the hollow fibers at a first location while the output lumen of the shaft is coupled to the hollow fibers at a second location disposed in the first direction from the first location.
Another aspect of the invention includes a method for exchanging heat with a body fluid in a body conduit. In this case, a catheter is provided with a plurality of hollow heat exchange fibers extending in fluid communication with an inlet lumen and an outlet lumen of the catheter. The heat exchange fibers collectively define a first cavity in heat transfer relationship with a body fluid in a body conduit.
In an additional aspect of the invention, an operative area of the catheter is sized and configured for disposition in a vessel containing blood. The operative area is adapted to perform a predetermined function, and the blood in the vessel has a tendency to form clots. In this aspect of the invention, the catheter is provided with a snare disposed relative to the operative area and being operable from a proximal end of the catheter to move from a low-profile state facilitating insertion of the catheter, to a high-profile state facilitating the capture of blood clots.
In still a further aspect of the invention, a heat exchange catheter is adapted for cooling the blood of a patient. The catheter includes a heat exchange region with a plurality of fibers each having a hollow configuration. A heat exchange fluid is disposed in the hollow fibers to cool the fibers and a coating is disposed on the outer surface of the fibers to inhibit formation of blood clots.
These and other features and advantages of the invention will be better understood with a description of the preferred embodiments of the invention and reference to the associated drawings.